Method for driving image pickup apparatus

ABSTRACT

A signal for focus detection is generated by a first operation, in which a signal of at least one photoelectric conversion element included in a photoelectric conversion unit is read to an input node of an amplification unit and the signal is supplied to a common output line by the amplification unit and signals for forming an image are generated by a second operation, in which a signal of another photoelectric conversion element included in the same photoelectric conversion unit as that including the at least one photoelectric conversion element from which the signal has been read in the first operation is read to the input node of the amplification unit while holding the signal read in the first operation using the amplification unit and the signals are supplied to the common output line by the amplification unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The embodiments relate to a method for driving an image pickupapparatus, and, more specifically, to a method for driving an imagepickup apparatus capable of performing focus detection in an imagepickup area.

2. Description of the Related Art

A remarkable development is currently seen in the field of image pickupapparatuses. An image pickup apparatus is known in which focus detectionadopting a pupil division method is performed using an image sensorobtained by forming a micro-lens in each pixel of the image pickupapparatus (Japanese Patent Laid-Open No. 2001-124984).

According to Japanese Patent Laid-Open No. 2001-124984, the image sensoris provided at an expected imaging area of an imaging lens. In addition,each pixel in the image sensor includes a photoelectric conversionelement A and a photoelectric conversion element B, and eachphotoelectric conversion element is arranged in such a way as to besubstantially conjugate to a pupil of the imaging lens with themicro-lenses of the image sensor formed on an imaging lens side.

Here, the photoelectric conversion element A receives a light beam thathas passed through a portion of the pupil of the imaging lens. On theother hand, the photoelectric conversion element B receives a light beamthat has passed through a portion of the pupil different from theportion through which the light beam received by the photoelectricconversion element A has passed. During the focus detection, signals areindependently read from the photoelectric conversion elements A and B ofa plurality of pixels, and two images are generated by the light beamsthat have passed through the different positions of the pupil of theimaging lens. In addition, image information can be obtained by addingthe signals of the two photoelectric conversion elements A and B.

Since the signals of the photoelectric conversion elements A and thesignals of the photoelectric conversion elements B are sequentially readindependently in Japanese Patent Laid-Open No. 2001-124984, the time atwhich the signals of the photoelectric conversion elements A arereceived and the time at which the signals of the photoelectricconversion elements B are received is different from each other.

More specifically, when a signal in a certain row is to be read, first,reset signals of the photoelectric conversion elements A are output.Next, light signals of the photoelectric conversion elements A areoutput. Similarly, reset signals of the photoelectric conversionelements B are output, and then light signals of the photoelectricconversion elements B are output. By this operation, a time differenceof tens to hundreds of microseconds is generated between the signals ofthe photoelectric conversion elements A and the signals of thephotoelectric conversion elements B. Therefore, an error is generatedbetween the signals of the photoelectric conversion elements A and thesignals of the photoelectric conversion elements B, which makes itdifficult to increase the accuracy of the focus detection.

SUMMARY OF THE INVENTION

One of the embodiments provides a method for driving an image pickupapparatus that includes a plurality of photoelectric conversion units,each including a plurality of photoelectric conversion elements, aplurality of amplification units, each of which is shared by theplurality of photoelectric conversion elements included in each of theplurality of photoelectric conversion units and amplifies signals of theplurality of photoelectric conversion elements, and a plurality ofcommon output lines that output signals obtained from the plurality ofamplification units. The method includes generating a signal for focusdetection by a first operation, in which a signal of at least one of theplurality of photoelectric conversion elements included in each of theplurality of photoelectric conversion units is read to an input node ofa corresponding one of the plurality of amplification units and thesignal is then supplied to a corresponding one of the plurality ofcommon output lines by the amplification unit, and generating signalsfor forming an image by a second operation, in which at least a signalof a photoelectric conversion element from which the signal has not beenread in the first operation and that is included in the samephotoelectric conversion unit as that including the at least onephotoelectric conversion element from which the signal has been read inthe first operation is read to the input node of the amplification unitand added with the signal read in the first operation while holding thesignal read in the first operation using the amplification unit and theadded signals are supplied to the common output line by theamplification unit.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the entirety of an image pickupapparatus according to a first embodiment.

FIG. 2 is a timing chart of the image pickup apparatus according to thefirst embodiment.

FIG. 3 is a block diagram illustrating the entirety of an image pickupapparatus according to a second embodiment.

FIG. 4 is a timing chart of the image pickup apparatus according to thesecond embodiment.

FIG. 5 is a block diagram illustrating pixels in an image pickupapparatus according to a third embodiment.

FIG. 6 is a timing chart of the image pickup apparatus according to thethird embodiment.

FIG. 7 is a block diagram illustrating pixels in an image pickupapparatus according to a fourth embodiment.

FIG. 8 is a timing chart of the image pickup apparatus according to thefourth embodiment.

DESCRIPTION OF THE EMBODIMENTS

Embodiments will be described with reference to the drawings. In thefollowing description, an example in which each pixel is configuredusing an n-channel metal-oxide-semiconductor (MOS) transistor will bedescribed. The embodiments may be applied to a case in which each pixelis configured using a p-channel MOS transistor. In this case, voltageand the like are changed as necessary.

First Embodiment

FIG. 1 is an equivalent circuit diagram of an image pickup apparatusaccording to the present embodiment. A photoelectric conversion unit 100includes a plurality of photoelectric conversion elements, namely afirst photoelectric conversion element 101A and a second photoelectricconversion element 101B here. As each photoelectric conversion element,a photodiode may be used.

Transfer transistors 102A and 102B are provided for the plurality ofphotoelectric conversion elements, respectively, and transfer signals ofthe corresponding photoelectric conversion elements to an input node 103of an amplification unit 104. A lens array (not illustrated) including aplurality of lenses is provided for each of a plurality of photoelectricconversion units above the photoelectric conversion elements. The lensesof each lens array focus light onto the plurality of photoelectricconversion elements in the same photoelectric conversion unit. Theplurality of photoelectric conversion elements included in eachphotoelectric conversion unit are provided at different positions whenviewed in plan.

The amplification unit 104 amplifies the signals transferred to theinput node 103 and outputs the signals to a common output line 107. AMOS transistor may be used for the amplification unit 104.

A reset transistor 105 supplies reset voltage to the input node 103 ofthe amplification unit 104. A selection transistor 106 controlselectrical continuity between the amplification unit 104 and the commonoutput line 107.

A current source 108 is electrically connected to the common output line107. The current source 108 supplies bias current to the amplificationunit 104, and a source follower can be configured by the amplificationunit 104 and the current source 108.

Drive lines 109A and 109B, a drive line 110, and a drive line 111 areconnected to the gates of the transfer transistors 102A and 102B, thereset transistor 105, and the selection transistor 106, respectively.Driving pulses are supplied, sequentially row by row or randomly, toeach gate from a vertical scanning circuit 112.

A column circuit receives signals from the common output line 107. Thecolumn circuit is connected to the common output line 107 directly,through a switch, or through a buffer. The signals processed by thecolumn circuit are sequentially output to an output amplifier 115 by ahorizontal scanning circuit 114 and then output to the outside.

A main operation of the column circuit is to execute invertingamplification on the signals from the common output line 107 using gaindetermined by a capacitance value of an input capacitor 116 and acapacitance value of a feedback capacitor 117. Furthermore, it ispossible to perform a virtual grounding operation. In addition, it ispossible to perform a correlated double sampling (CDS) operation througha clamping operation using the input capacitor 116.

Next, an example of the column circuit will be described. A first nodeof the input capacitor 116 is electrically connected to the commonoutput line 107, and a second node of the input capacitor 116 iselectrically connected to an inverting input node of an operationalamplifier 119. A first node of the feedback capacitor 117 iselectrically connected to the inverting input and the second node of theinput capacitor 116. A second node of the feedback capacitor 117 iselectrically connected to an output node of the operational amplifier119.

A switch 118 is provided along a feedback path between the invertinginput node and the output node of the operational amplifier 119 in orderto control an electrical connection between the two. The feedbackcapacitor 117 and the switch 118 are provided parallel to each other.

A power supply 120 supplies reference voltage Vref to a non-invertinginput node of the operational amplifier 119. Storage capacitors 121 to124 are capacitors that store outputs of the operational amplifier 119.Switches 125 to 128 are provided along electrical paths between thestorage capacitors 121 to 124 and the operational amplifier 119,respectively, and control electrical continuity between the output nodeof the operational amplifier 119 and the storage capacitors 121 to 124,respectively. Switches 129 to 132 receive signals from the horizontalscanning circuit 114 and output the signals stored in the storagecapacitors 121 to 124, respectively, to horizontal output lines 139 and140.

The output amplifier 115 is provided as necessary. The output amplifier115 obtains a difference between the signals output from the columncircuit to the horizontal output lines 139 and 140 and outputs thedifference to the outside.

A driving pulse PCOR is supplied to the switch 118. A driving pulse PTNis supplied to the switches 126 and 128. A driving pulse PTSA issupplied to the switch 125. A driving pulse PTSAB is supplied to theswitch 127.

Next, driving of the image pickup apparatus illustrated in FIG. 1 willbe described with reference to FIG. 2. The driving pulses cause thecorresponding elements to be conductive at high level.

First, at a time T=t1, driving pulses PTXA and PTXB supplied to thedrive lines 109A and 109B, respectively, are switched to the high level.At this time, because a driving pulse PRES supplied to the drive line110 is at the high level, the photoelectric conversion elements 101A and101B are reset.

Next, at a time T=t2, the driving pulses PTXA and PTXB are switched tolow level. Charge storage periods of the photoelectric conversionelements 101A and 101B begin at this timing. Since the driving pulsePRES remains at the high level, a reset operation for the input node 103of the amplification unit 104 continues.

After storage is performed for a certain period of time, signals aresupplied to the common output line 107 row by row or in a plurality ofrows at a time.

At a time T=t3, a driving pulse PSEL supplied to the drive line 111 ofthe selection transistor 106 is switched to the high level, and theselection transistor 106 becomes conductive. Therefore, a signalaccording to the potential of the input node 103 of the amplificationunit 104 is output to the common output line 107.

By switching the driving pulse PRES supplied to the drive line 110 ofthe reset transistor 105 to the low level at a time T=t4, the resetoperation for the input node 103 of the amplification unit 104 iscancelled. A reset signal level is then supplied to the common outputline 107 and input to the column circuit. At this time, the operationalamplifier 119 is in a virtual grounding state. More specifically, thedriving pulse PCOR is at the high level, and the switch 118 is closed.The operational amplifier 119 is in a state in which the outputreference voltage Vref is buffered, and the reset signal level issupplied to the input capacitor 116 in this state.

Next, the driving pulse PCOR is switched to the low level at a timeT=t5, and the driving pulse PTN is switched from the low level to thehigh level at a time T=t6 in order to close the switches 126 and 128.The driving pulse PTN is switched from the high level to the low levelat a time T=t7 in order to open the switches 126 and 128. By thisoperation, the output reference voltage Vref is substantially suppliedto the storage capacitors 122 and 124, and then the storage capacitors122 and 124 and the output node of the operational amplifier 119 becomenon-conductive.

At a time T=t8, the driving pulse PTXA is switched to the high level andoptical charge of the first photoelectric conversion element 101A istransferred to the input node 103 of the amplification unit 104, and, ata time T=t9, the driving pulse PTXA is switched to the low level. Bythis operation, the optical charge of the first photoelectric conversionelement 101A is transferred to the input node 103. Therefore, a signalbased on the optical charge is supplied to the column circuit by theamplification unit 104 and the common output line 107. By thisoperation, a signal for focus detection can be generated in the commonoutput line 107.

The column circuit outputs a value obtained by multiplying a change involtage by inverse gain at a ratio of a capacitance value C0 of theinput capacitor 116 to a capacitance value Cf of the feedback capacitor117. More specifically, when a change in the voltage of the commonoutput line 107 is denoted by ΔVa (negative) and the output of theoperational amplifier 119 is denoted by V(A), the following expression(1) is obtained:V(A)=Vref+ΔVA×(−C0/Cf)   (1)

Next, at a time T=t10, the driving pulse PTSA is switched from the lowlevel to the high level to close the switch 125. At a time T=t11, thedriving pulse PTSA is switched from the high level to the low level toopen the switch 125. By this operation, the storage capacitor 121 storesa signal.

At a time T=t12, the driving pulse PTXA is switched to the high level,and the driving pulse PTXB is switched to the high level at least for apart of a period in which the driving pulse PTXA is at the high level.By this operation, optical charges of both the photoelectric conversionelements 101A and 101B can be simultaneously transferred to the inputnode 103. By this operation, a signal for forming an image can begenerated in the common output line 107. The input node 103 of theamplification unit 104 is not reset until the optical charges of boththe photoelectric conversion elements 101A and 101B are simultaneouslytransferred to the input node 103 after the signal of the photoelectricconversion element 101A is transferred.

The charges transferred to the input node 103 of the amplification unit104 are supplied to the column circuit, just as when only the charge ofthe photoelectric conversion element 101A is transferred. When a changein the potential of the common output line 107 is denoted by ΔVa+b(negative) and the output potential of the operational amplifier 119 isdenoted by V(A+B), the following expression (2) is obtained:V(A+B)=Vref+ΔVa+b×(−C0/Cf)  (2)

At a time T=t14, the driving pulse PTSAB is switched from the low levelto the high level to close the storage capacitor 122. Next, at a timeT=t15, the driving pulse PTSAB is switched from the high level to thelow level to open the storage capacitor 122. By this operation, thepotential V(A+B) of the output node of the operational amplifier 119 canbe written to the storage capacitor 123.

Therefore, a difference voltage between capacitances CTSAB and CTN canbe obtained by the following expression (3):V(A+B)−Vref=ΔVa+b×(−C0/Cf)   (3)This corresponds to a result obtained by adding the signals of twophotoelectric conversion elements included in a photoelectric conversionunit. A signal corresponding to one pixel when an image is capturedusing a plurality of photoelectric conversion elements included in aphotoelectric conversion unit is obtained.

In addition, by obtaining a potential difference between the storagecapacitors 121 and 122, which is obtained by the following expression(4), a signal of only the photoelectric conversion element 101A can beobtained:V(A)−Vref=ΔVa×(−C0/Cf)   (4)The signal obtained by the photoelectric conversion element 101Acorresponds to information regarding a focused light beam that haspassed through a part of a pupil of an imaging lens. Furthermore, byobtaining a potential difference between the two, which is obtained bythe following expression (5), a signal of only the photoelectricconversion element 101B can be obtained:(ΔVa+b×(−C0/Cf))−(ΔVa×(−C0/Cf))=(ΔVa+b−ΔVa)×(−C0/Cf)   (5)The signal obtained by the photoelectric conversion element 101Bcorresponds to information regarding a focused light beam that haspassed through a part of the pupil of the imaging lens. The plurality ofphotoelectric conversion elements included in each photoelectricconversion unit are provided at different positions when viewed in plan.Focus detection can be performed on the basis of the pieces ofinformation of the photoelectric conversion elements 101A and 101Bregarding the two light beams.

The above calculation may be performed inside the image pickup apparatusor may be performed by a signal processing unit after the relevantsignals are output from the image pickup apparatus. However, the signalof only the photoelectric conversion element 101A and the resultobtained by adding the signals of the photoelectric conversion elements101A and 101B are obtained in the image pickup apparatus.

Next, at a time T=t16, the driving pulse PRES is switched to the highlevel to cause the reset transistor 105 to be conductive and reset thepotential of the input node 103.

The signals stored in the storage capacitors 121 to 124 are read bysequentially causing driving pulses 133 and 134 synchronized with apulse PH to be conductive after a time T=t17. According to the presentembodiment, since the output amplifier 115 that can execute a differenceprocess is provided in a later stage of the horizontal output lines 139and 140, a difference between the signals stored in the storagecapacitors 121 and 122 can be output to the outside of the image pickupapparatus. Furthermore, a difference between the signals stored in thestorage capacitors 123 and 124 can be output to the outside of the imagepickup apparatus. Therefore, noise generated in the horizontal outputlines 139 and 140 can be reduced. However, the output amplifier 115 neednot necessarily have a configuration in which a differential output isobtained, and may be simply a buffer stage. Furthermore, the outputamplifier 115 need not be provided. Thereafter, signals in the rows aresequentially scanned by the horizontal scanning circuit 114 and suppliedto the horizontal output lines 139 and 140.

It is to be noted that an example in which, as the order of reading, theadded signals of the photoelectric conversion elements 101A and 101B areread after the signal of only the photoelectric conversion element 101Ais read has been described, the order may be switched. By reading thesignal of only the photoelectric conversion element 101A first, bettersignals can be obtained. This is because the signals are moresusceptible to leakage current due to the capacitors and the switcheswhen a period for which the signals are stored in the storage capacitors121 to 124 is longer.

The characteristics of the present embodiment lie in the operations in aperiod from the time t11 to the time t15.

In Japanese Patent Laid-Open No. 2001-124984, the following operation isdisclosed. A signal of a first photoelectric conversion element iswritten to a storage capacitor, a horizontal transfer operation isperformed, and the signal is read out to the outside of an image pickupapparatus. Next, a reset transistor executes a reset operation.Thereafter, a signal of a second photoelectric conversion element iswritten to the storage capacitor, the horizontal transfer operation isperformed, and the signal is read out to the outside of a sensor. Thereset transistor then executes the reset operation again.

In this case, a reading time difference (tens to hundreds ofmicroseconds) corresponding to one row is undesirably generated betweenthe reading of the signal of the first photoelectric conversion elementand the reading of the signal of the second photoelectric conversionelement.

In the present embodiment, when the signal of the photoelectricconversion element 101A has been read, the signal is written to astorage capacitor at the time T=t11. At the time T=t12, while the signalof the photoelectric conversion element 101A remains held at the inputnode 103, the signals of both the photoelectric conversion elements 101Aand 101B are read at the time T=t12. In doing so, the reading time canbe significantly (several microseconds) decreased. Furthermore, the timedifference in the signal reading between the photoelectric conversionelements 101A and 101B can decrease, thereby increasing the accuracy ofthe focus detection.

In addition, the secondary characteristics of the present embodiment liein the operations in a period from the time T=t8 to the time T=t15. Bysimultaneously switching the driving pulses PTXA and PTXB to the highlevel, the following effects can be produced. However, the driving pulsePTXA need not be necessarily switched to the high level in a secondoperation.

First, as a first effect, the potential of the input node 103 increasesbecause of capacitive coupling between a drive line of a transfertransistor and the input node 103 when the gate potential of thetransfer transistor switches from the low level to the high level. Inthe present embodiment, the gate potential of the two transfertransistors 102A and 102B switches from the low level to the high level.Therefore, an increase in the potential of the input node 103 is largerthan when only one transfer transistor is used. When the potential ofthe input node 103 has become high, it becomes easier for the charges ofthe photoelectric conversion elements 101A and 101B to be transferred tothe input node 103. Therefore, the transfer efficiency can be improved.

In particular, when one pixel for capturing an image has been dividedinto two photoelectric conversion elements as in the configuration ofthe image pickup apparatus according to the present embodiment, apotential barrier for signal charge is often provided between thephotoelectric conversion elements 101A and 101B. Due to this potentialbarrier, the potential distribution of the photoelectric conversionelements 101A and 101B becomes complex. Therefore, residual charge aftertransfer tends to be generated, and accordingly fixed pattern noise orrandom noise can be generated. On the other hand, by switching thedriving pulses PTXA and PTXB to the high level at the same time, aneffect can be produced in which the fixed pattern noise or the randomnoise is reduced while the potential of the input node is high.

As a second effect, a difference in storage time between thephotoelectric conversion elements 101A and 101B can be decreased. Forexample, in the configuration disclosed in Japanese Patent Laid-Open No.2001-124984, the storage times of the two photoelectric conversionelements undesirably become different from each other. On the otherhand, as in the present embodiment, by making the timings at which alltransfer gates corresponding to photoelectric conversion elements usedto add signals are turned off be substantially the same when the inputnode 103 adds the signals, the storage times can be the same. This isespecially effective in a configuration in which a signal for the focusdetection is obtained in an image pickup area of the image pickupapparatus.

Although a signal of a single photoelectric conversion element is usedto generate a signal for the focus detection in the present embodiment,signals of a plurality of photoelectric conversion elements may be usedwhen a larger number of photoelectric conversion elements are includedin one photoelectric conversion unit. However, signals of all thephotoelectric conversion elements included in one photoelectricconversion unit cannot be used to obtain a signal for the focusdetection. This holds true for the following embodiments.

In addition, although signals of all the photoelectric conversionelements (two here) included in one photoelectric conversion unit areread in the second operation, the method for reading signals is notlimited to this. It is sufficient if a signal of a photoelectricconversion element that has not read in a first operation is read. This,too, holds true for the following embodiments.

Second Embodiment

FIG. 3 is an equivalent circuit diagram of an image pickup apparatusaccording to a second embodiment.

A difference from the first embodiment is the configurations of thephotoelectric conversion unit and the column circuit. The number ofphotoelectric conversion elements included in one photoelectricconversion unit is 3, and accordingly the number of storage capacitorsincluded in the column circuit is 6. Components having the samefunctions as in the first embodiment are given the same referencenumerals, and detailed description thereof is omitted.

A photoelectric conversion unit 200 includes photoelectric conversionelements 101A to 101C. Since the number of photoelectric conversionelements included in one pixel for capturing an image is larger thanthat in the first embodiment, more accurate focus detection is possible.

Transfer transistors 102A to 102C that transfer charges of thephotoelectric conversion elements 101A to 101C are included. As adriving pulse for the transfer transistor 102C, a driving pulse PTXC isadded.

A column circuit 210 includes a storage capacitor 201 for storingsignals of the photoelectric conversion element 101A to 101C added toone another. In addition, a storage capacitor 202 for storing a noiselevel is included. Switches 203 to 206 corresponding to these componentsare also included.

Next, a method for driving the image pickup apparatus according to thepresent embodiment will be described with reference to FIG. 4. Because abasic operation is the same as that described with reference to FIG. 2,differences from the first embodiment will be mainly described.

At the time T=t12, both the driving pulses PTXA and PTXB are switched tothe high level. By this operation, the signals of the photoelectricconversion elements 101A and 101B are added at the input node 103.Although both the driving pulses PTXA and PTXB are switched to the highlevel here, only the driving pulse PTXB may be switched to the highlevel. Next, at the time T=t16, all of the driving pulses PTXA, PTXB,and PTXC are switched to the high level. By this operation, the chargesof the photoelectric conversion elements 101A to 101C are added at theinput node 103. At the time T=t17, all of the driving pulses PTXA, PTXB,and PTXC are switched to the low level. By this operation, the storageperiods of the photoelectric conversion elements 101A to 101C can be thesame, namely as a period from the time t2 to the time t17.

After the added signals of the photoelectric conversion elements 101A to101C are read, a signal of only the photoelectric conversion element101A or added signals of the photoelectric conversion elements 101A and101B may be read.

By reading the signal of only the photoelectric conversion element 101A,the added signals of the photoelectric conversion elements 101A and101B, and the added signals of the photoelectric conversion elements101A to 101C in this order, better signals can be obtained. This isbecause the signals are more susceptible to leakage current due to thecapacitors and the switches when a period for which the signals arestored in the storage capacitors 121 to 124, 201, and 202 is longer.

Third Embodiment

FIG. 5 is an equivalent circuit diagram of an image pickup apparatusaccording to a third embodiment. A difference from the first and secondembodiments is that the amplification unit 104 is shared by a pluralityof photoelectric conversion elements included in different photoelectricconversion units.

In FIG. 5, a first photoelectric conversion unit including photoelectricconversion elements 501A and 501B and a second photoelectric conversionunit including photoelectric conversion elements 502A and 502B areincluded. Light collected by a first micro-lens is incident on theplurality of photoelectric conversion elements 501A and 501B included inthe first photoelectric conversion unit and light collected by a secondmicro-lens is incident on the plurality of photoelectric conversionelements 502A and 502B included in the second photoelectric conversionunit.

Transfer transistors 503A, 503B, 504A, and 504B are provided for thephotoelectric conversion elements 501A, 501B, 502A and 502B,respectively. As lines for supplying driving pulses to the transfertransistors 503A, 503B, 504A, and 504B, drive lines 505A, 505B, 506A,and 506B, respectively, are provided.

According to this configuration, the amplification unit 104, the resettransistor 105, and the selection transistor 106 can be shared by aplurality of pixels for capturing an image. In doing so, the number oftransistors included in one pixel for capturing an image can bedecreased. As a result, the area of the photoelectric conversionelements can be increased.

With respect to an operation for sequentially reading the photoelectricconversion elements 501A, 501B, 502A, and 502B, signals can be read assignals in different rows by performing an operation that is basicallythe same as the reading described with reference to FIG. 2. Morespecifically, after a signal of the photoelectric conversion element501A is read in the first photoelectric conversion unit, signals of thephotoelectric conversion elements 501A and 501B are added to each otherat the input node 103. In doing so, both a signal for the focusdetection and signals for capturing an image can be generated. Next,after a signal of the photoelectric conversion element 502A is read inthe second photoelectric conversion unit, signals of the photoelectricconversion elements 502A and 502B are added to each other at the inputnode 103. In doing so, both a signal for the focus detection and signalsfor capturing an image can be generated.

Furthermore, in the present embodiment, the amplification unit 104 isshared by the two photoelectric conversion units that are different fromeach other. Therefore, the signals of the photoelectric conversionelements 501A and 502A are added at the input node 103 and signals ofthe photoelectric conversion elements 501B and 502B may be added to eachother at the input node 103. A specific example of a driving timing isillustrated in FIG. 6. Characteristics of the present embodiment will bemainly described. Here, a driving pulse PTXA (505A) is supplied to thetransfer transistor 503A, and a driving pulse PTXB (505B) is supplied tothe transfer transistor 503B. Furthermore, a driving pulse PTXA (506A)is supplied to the transfer transistor 504A, and a driving pulse PTXB(506B) is supplied to the transfer transistor 504B.

At the time T=t8, the driving pulses PTXA (505A) and PTXA (506A) areswitched from the low level to the high level. Thereafter, at the timeT=t9, the driving pulses PTXA (505A) and PTXA (506A) are switched fromthe high level to the low level. By this operation, the signals of thephotoelectric conversion element 501A and 502A included in differentphotoelectric conversion units are added to each other at the input node103. These signals can be used as the signals for the focus detection.

Next, at the time T=t12, the driving pulses PTXA (505A), PTXB (505B),PTXA (506A), and PTXB (506B) are switched from the low level to the highlevel. Thereafter, at the time T=t13, the driving pulses PTXA (505A),PTXB (505B), PTXA (506A), and PTXB (506B) are switched from the lowlevel to the high level. By this operation, the signals of all thephotoelectric conversion elements 501A, 501B, 502A, and 502B included indifferent photoelectric conversion units are added to each other at theinput node 103. These signals are used as the signals for capturing animage.

Since the signals for the focus detection are obtained by adding signalsof a plurality of photoelectric conversion elements included indifferent photoelectric conversion units with one another through thisoperation, the S/N ratio improves. Therefore, more accurate focusdetection is possible.

It is to be noted that although an example in which signals of twopixels for capturing an image are added to each other has been describedin the present embodiment, the same effect can be produced even when thenumber of pixels is 3 or more.

Fourth Embodiment

FIG. 7 is an equivalent circuit diagram of an image pickup apparatusaccording to a fourth embodiment. A difference of the present embodimentfrom the third embodiment is that a switch for electrically connecting aplurality of input nodes 103 to one another is provided. Componentshaving functions similar to those of the configurations according to thefirst to third embodiments are given similar reference numerals, anddetailed description thereof is omitted.

In FIG. 7, a first photoelectric conversion unit includes photoelectricconversion elements 701A and 701B. A second photoelectric conversionunit includes photoelectric conversion elements 702A and 702B. A thirdphotoelectric conversion unit includes photoelectric conversion elements721A and 721B. A fourth photoelectric conversion unit includesphotoelectric conversion elements 722A and 722B. An amplification unit707 shared by the first and second photoelectric conversion units isprovided. An amplification unit 727 shared by the third and fourthphotoelectric conversion units is provided.

Transfer transistors 703A, 703B, 704A, 704B, 723A, 723B, 724A, and 724Bare provided for these photoelectric conversion elements, respectively.Drive lines 705A, 705B, 706A, 706B, 725A, 725B, 726A, and 726B fordriving these transfer transistors, respectively, are provided.

A switch 740 electrically connects input nodes of the amplificationunits 707 and 727 to each other. The switch 740 is controlled by a driveline 741.

FIG. 8 is a driving pulse diagram of FIG. 7. Here, only elementscorresponding to the first photoelectric conversion unit and the thirdphotoelectric conversion unit will be extracted and described. Thesecond and fourth photoelectric conversion units can perform the samedriving. A driving pulse PTXA (705A) is a pulse supplied to the driveline 705A. A driving pulse PTXB (705B) is a pulse supplied to the driveline 705B. A driving pulse PTXA (725A) is a pulse supplied to the driveline 725A. A driving pulse PTXB (725B) is a pulse supplied to the driveline 725B. A driving pulse PVADD (741) is a pulse supplied to the driveline 741.

In FIG. 8, an example in which signals of the photoelectric conversionelements 701A and 721A included in the first photoelectric conversionunit and the third photoelectric conversion unit, respectively, areadded to each other is illustrated.

The driving pulse PVADD (741) is kept at the high level during a periodillustrated in FIG. 8. That is, the inputs nodes of the amplificationunits 707 and 727 are electrically connected to each other constantly.

At the time T=t8, the driving pulses PTXA (705A) and PTXA (725A) areswitched from the low level to the high level. Thereafter, at the timeT=t9, the driving pulses PTXA (705A) and PTXA (725A) are switched fromthe high level to the low level. By this operation, the signals of thephotoelectric conversion elements 701A and 721A included in differentphotoelectric conversion units are transferred to the correspondingamplification units 707 and 727, respectively. Since the switch 740 isclosed, the signals are added to each other. These signals can be usedas the signals for the focus detection.

Next, at the time T=t12, the driving pulses PTXA (705A), PTXB (705B),PTXA (725A), and PTXB (725B) are switched from the low level to the highlevel. Thereafter, at the time T=t13, the driving pulses PTXA (705A),PTXB (705B), PTXA (725A), and PTXB (725B) are switched from the highlevel to the low level. By this operation, signals of the plurality ofphotoelectric conversion elements 701A, 701B, 721A, and 721B included indifferent photoelectric conversion units are transferred to thecorresponding amplification units 707 and 727. Since the switch 740 isclosed, all the signals are added to one another. These signals can beused as the signals for capturing an image.

In the present embodiment, the switch for electrically connecting theplurality of input nodes is added. This is desirable when signals of thesame color are separated from one another in an image pickup apparatusincluding color filters, that is, for example, when the image pickupapparatus includes color filters arranged in a Bayer pattern. This isbecause it is possible to add the signals of photoelectric conversionelements of the same color that are arranged separately from one anotherto one another. Therefore, not only the focus detection but also the S/Nratio of image signals can be improved, thereby realizing accurate focusdetection while obtaining high-quality image information.

It is to be noted that although an example in which two input nodes areconnected to each other has been described in the present embodiment,the same effect can be produced even when the number of input nodesconnected to one another is 3 or more.

Although the specific embodiments have been described, the presentinvention is not limited to the above embodiments and may be modified oraltered in various ways. For example, the circuit configurations ofpixels are not limited to those described above, and a configuration inwhich selection and deselection are switched by switching the potentialof an input node using a reset unit without including a selection unitmay be adopted. Furthermore, although a configuration in which anoperational amplifier is included as a column circuit has beendescribed, a simple configuration such as that of a common-sourceamplification circuit may be adopted, instead. Alternatively, variousmodifications are possible such as a configuration in which a pluralityof gain stages are provided and a configuration in which an addingbetween a gain stage and a buffer stage is used. In addition, althoughone common output line is provided for a pixel column in the aboveembodiments, a plurality of common output lines may be provided for onepixel column.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2011-248823 filed Nov. 14, 2011, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A method for driving an image pickup apparatusthat includes a plurality of photoelectric conversion units, eachincluding a plurality of photoelectric conversion elements, a pluralityof amplification units, each of which is shared by the plurality ofphotoelectric conversion elements included in each of the plurality ofphotoelectric conversion units and amplifies signals of the plurality ofphotoelectric conversion elements, and a plurality of common outputlines that output signals obtained from the plurality of amplificationunits, the method comprising: generating a signal for focus detection bya first operation, in which a signal of at least one of the plurality ofphotoelectric conversion elements included in each of the plurality ofphotoelectric conversion units is read to an input node of acorresponding one of the plurality of amplification units and the signalis then supplied to a corresponding one of the plurality of commonoutput lines by the amplification unit; and generating a signal forforming an image by a second operation, in which at least a signal of aphotoelectric conversion element from which the signal has not been readin the first operation and that is included in the same photoelectricconversion unit as that including the at least one photoelectricconversion element from which the signal has been read in the firstoperation is read to the input node of the amplification unit and addedwith the signal read in the first operation while holding the signalread in the first operation using the amplification unit and the addedsignals are supplied to the common output line by the amplificationunit.
 2. The method for driving an image pickup apparatus according toclaim 1, wherein a potential of the input node of the amplification unitis not reset in a period between the first operation and the secondoperation.
 3. The method for driving an image pickup apparatus accordingto claim 1, wherein the image pickup apparatus includes a lens arrayincluding a plurality of lenses provided for each of the plurality ofphotoelectric conversion units, and the lenses of each lens array focuslight onto the plurality of photoelectric conversion elements includedin the same photoelectric conversion unit.
 4. The method for driving animage pickup apparatus according to claim 1, wherein one of theplurality of amplification units is shared by a plurality ofphotoelectric conversion elements included in different photoelectricconversion units.
 5. The method for driving an image pickup apparatusaccording to claim 4, wherein, in the first operation, a signal of atleast one photoelectric conversion element included in a firstphotoelectric conversion unit and a signal of at least one photoelectricconversion element included in a second photoelectric conversion unitare added to each other by one of the plurality of amplification unitsshared by the first and second photoelectric conversion units, andwherein, in the second operation, signals of a plurality ofphotoelectric conversion elements included in the first photoelectricconversion unit and signals of a plurality of photoelectric conversionelements included in the second photoelectric conversion unit are addedto one another by the one of the plurality of amplification units sharedby the first and second photoelectric conversion units.
 6. The methodfor driving an image pickup apparatus according to claim 1, wherein theimage pickup apparatus includes a switch that electrically connectsinput nodes of the plurality of amplification units to one another. 7.The method for driving an image pickup apparatus according to claim 6,wherein, by closing the switch in the first operation, the input nodesof the plurality of amplification units are electrically connected toone another and signals of the input nodes connected to one another areadded to one another, and wherein, by closing the switch in the secondoperation, the input nodes of the plurality of amplification units areelectrically connected to one another and signals of the input nodesconnected to one another are added to one another.
 8. The method fordriving an image pickup apparatus according to claim 1, wherein theimage pickup apparatus includes a plurality of transfer gates, each ofwhich transfers a signal of each of the plurality of photoelectricconversion elements to an input node of a corresponding one of theplurality of amplification units, and wherein, in the second operation,one of a plurality of transfer gates corresponding to a photoelectricconversion element from which a signal is transferred in the secondoperation is conductive for at least a part of a period in which one ofa plurality of transfer gates corresponding to a photoelectricconversion element from which a signal is transferred in the firstoperation is conductive.
 9. The method for driving an image pickupapparatus according to claim 1, wherein the plurality of photoelectricconversion elements included in each of the plurality of photoelectricconversion units are provided at different positions when viewed inplan.
 10. The method for driving an image pickup apparatus according toclaim 1, wherein potential of the input node of the amplification unitis reset before the first operation, and a difference process isperformed on the signals obtained by the first operation and the secondoperation using a reset signal output to the common output line by theamplification unit after the resetting.
 11. A method for driving animage pickup apparatus that includes a plurality of photoelectricconversion units, each including a plurality of photoelectric conversionelements, a plurality of amplification units, each of which is shared bythe plurality of photoelectric conversion elements included in each ofthe plurality of photoelectric conversion units and amplifies signals ofthe plurality of photoelectric conversion elements, and a plurality ofcommon output lines that output signals obtained from the plurality ofamplification units, the method comprising: generating a signal forfocus detection by a first operation, in which a signal of at least oneof the plurality of photoelectric conversion elements included in eachof the plurality of photoelectric conversion units is read to an inputnode of a corresponding one of the plurality of amplification units andthe signal is then supplied to a corresponding one of the plurality ofcommon output lines by the amplification unit; and generating a signalfor forming an image by a second operation, in which at least a signalof a photoelectric conversion element from which the signal has not beenread in the first operation and that is included in the samephotoelectric conversion unit as that including the at least onephotoelectric conversion element from which the signal has been read inthe first operation is read to the input node of the amplification unitand added to the signal read in the first operation while holding thesignal read in the first operation using the amplification unit and theadded signals are supplied to the common output line by theamplification unit, wherein, in the second operation, one of a pluralityof transfer gates corresponding to a photoelectric conversion elementfrom which a signal is transferred in the second operation is conductivefor at least a part of a period in which one of a plurality of transfergates corresponding to a photoelectric conversion element from which asignal is transferred in the first operation is conductive, and whereinpotential of the input node of the amplification unit is reset beforethe first operation, and a difference process is performed on thesignals obtained by the first operation and the second operation using areset signal output to the common output line by the amplification unitafter the resetting.
 12. An image pickup apparatus comprising: aplurality of photoelectric conversion units, each including a pluralityof photoelectric conversion elements; a plurality of amplificationunits, each of which is shared by the plurality of photoelectricconversion elements included in each of the plurality of photoelectricconversion units and amplifies signals of the plurality of photoelectricconversion elements; and a plurality of common output lines configuredto output signals obtained from the plurality of amplification units,wherein a signal for focus detection is generated by a first operation,in which a signal of at least one of the plurality of photoelectricconversion elements included in each of the plurality of photoelectricconversion units is read to an input node of a corresponding one of theplurality of amplification units and the signal is then supplied to acorresponding one of the plurality of common output lines by theamplification unit, and wherein signals for forming an image aregenerated by a second operation, in which at least a signal of aphotoelectric conversion element from which the signal has not been readin the first operation and that is included in the same photoelectricconversion unit as that including the at least one photoelectricconversion element from which the signal has been read in the firstoperation is read to the input node of the amplification unit and addedto the signal read in the first operation while holding the signal readin the first operation using the amplification unit and the addedsignals are supplied to the common output line by the amplificationunit.
 13. An image pickup apparatus comprising: a plurality ofphotoelectric conversion units, each including a plurality ofphotoelectric conversion elements; a plurality of amplification units,each of which is shared by the plurality of photoelectric conversionelements included in each of the plurality of photoelectric conversionunits and amplifies signals of the plurality of photoelectric conversionelements; and a plurality of common output lines configured to outputsignals obtained from the plurality of amplification units, wherein asignal for focus detection is generated by a first operation, in which asignal of at least one of the plurality of photoelectric conversionelements included in each of the plurality of photoelectric conversionunits is read to an input node of a corresponding one of the pluralityof amplification units and the signal is then supplied to acorresponding one of the plurality of common output lines by theamplification unit, wherein signals for forming an image are generatedby a second operation, in which at least a signal of a photoelectricconversion element from which the signal has not been read in the firstoperation and that is included in the same photoelectric conversion unitas that including the at least one photoelectric conversion element fromwhich the signal has been read in the first operation is read to theinput node of the amplification unit and added to the signal read in thefirst operation while holding the signal read in the first operationusing the amplification unit and the added signals are supplied to thecommon output line by the amplification unit, wherein a lens arrayincluding a plurality of lenses provided for each of the plurality ofphotoelectric conversion units is included, and the lenses of each lensarray focus light onto the plurality of photoelectric conversionelements that are included in the same photoelectric conversion unit andthat are provided at different positions when viewed in plan, wherein aplurality of transfer gates, each of which transfers a signal of each ofthe plurality of photoelectric conversion elements to an input node of acorresponding one of the plurality of amplification units, are included,wherein, in the second operation, one of the plurality of transfer gatescorresponding to a photoelectric conversion element from which a signalis transferred in the second operation is conductive for at least a partof a period in which one of the plurality of transfer gatescorresponding to a photoelectric conversion element from which a signalis transferred in the first operation is conductive, and whereinpotential of the input node of the amplification unit is reset beforethe first operation, and a difference process is performed on thesignals obtained by the first operation and the second operation using areset signal output to the common output line by the amplification unitafter the resetting.